Impairment Mechanisms for SSB Mobile Communications at UHF with Pilot-Based Doppler/Fading Correction

Abstract

Several impairments are associated with the pilot-based correction of a single sideband (SSB) voice signal for the effects of vehicle motion in a Rayleigh multipath field. These include the distortion caused by a limit on the available correction gain, the distortion resulting from frequency selective fading, the degradation of the signal-to-interference (S/I) [noise (S/N)] ratio, and the distortion induced because of interference to the pilot from a cochannel pilot or from noise. We have investigated these impairments for a specific feedforward, phase- and gain-correcting, ideal receiver. For this receiver, the S/I ratio is degraded at baseband because of the time-varying nature of the gain correction signal and the assumption that the correction signal is correlated with the desired voice signal fading envelope but is independent of the interferer fading envelope. A limit on correction gain appears necessary to limit the magnitude of several of the impairments, and has been considered as a parameter in the analysis of each impairment type. The results are here extended to characterize an “equal-gain” space diversity receiver. Diversity combining is applied after phase correction, but before gain correction to maintain proper voice correction while retaining the benefits of the improved envelope statistics. This paper deals only with the SSB idealized channel, not with a system employing SSB modulation; the authors recognize that many complicated systems problems (eg., antenna combining, channel generation, and cost reduction) must be solved before a working system using the channel analyzed herein can become a reality.